A troubled Muscatine teenager who allegedly shared his online plot of a "Columbine-type massacre" at his former high school was arrested and charged with terrorism Wednesday, one day before he threatened to carry out his plan, authorities said.

Crude explosives were seized at the home of 17-year-old Christopher Dewayne Titus, a self-proclaimed white supremacist, Muscatine County Attorney Gary Allison said.

Police said they were tipped off to Titus' plan when a 19-year-old Knoxville woman informed authorities Tuesday of Titus' threats after he shared his plans with her through e-mails and online chats. Titus allegedly told the girl he would carry out his threats on March 2.

Within a day, Muscatine police traced the e-mails and online chats to Titus. He was arrested early Wednesday morning at the home he shares with his parents.

Titus was charged with threats of terrorism and threats of arson, both Class D felonies.

Allison said another 18-year-old who may have been in on the alleged plot is being questioned by authorities.

Titus dropped out of Muscatine High School a year ago, and has a lengthy criminal history, Allison said. His ties to white supremacy may be a motivating factor in the plotted attack.

"He has a lot of tattoos and carvings on his arms that are swastikas and other kinds of white power symbols. It certainly seems to be a driving factor," Allison said. "He was also kind of into the Gothic thing, and the Columbine shooters tended to be heroes of his."

Eric Harris and Dylan Klebold killed 13 people before committing suicide in an April 20, 1999, shooting spree at Columbine High School in Littleton, Colo.

Muscatine High School Principal Robert Weaton declined comment, referring questions to Superintendent Tom Williams. A phone call to Williams was not returned Wednesday night.